The invention generally relates to length-changing actuators such as a magnetorestrictive or length-changing solid state actuator. In particular, the present invention relates to a compensator assembly for a length-changing actuator, and more particularly to an apparatus and method for hydraulically compensating a solid state actuated high-pressure fuel injector for internal combustion engines.
Solid-state actuator such as a length-changing actuator may include a ceramic structure whose axial length can change through the application of an operating voltage. It is believed that in typical applications, the axial length can change by, for example, approximately 0.12%. In a stacked configuration, it is believed that the change in the axial length is magnified as a function of the number of actuators in the length-changing actuator stack. Because of the nature of the length-changing actuator, it is believed that a voltage application results in an instantaneous expansion of the actuator and an instantaneous movement of any structure connected to the actuator. In the field of automotive technology, especially, in internal combustion engines, it is believed that there is a need for the precise opening and closing of an injector valve element for optimizing the spray and combustion of fuel. Therefore, in internal combustion engines, length-changing actuators are now employed for the precise opening and closing of the injector valve element.
During operation, components of an internal combustion engine experience significant thermal fluctuations that result in the thermal expansion or contraction of the engine components. For example, it is believed that a fuel injector assembly includes a valve body that may expand during operation due to the heat generated by the engine. Moreover, it is believed that a valve element operating within the valve body may contract due to contact with relatively cold fuel. If a length-changing actuator stack is used for the opening and closing of an injector valve element, it is believed that the thermal fluctuations can result in valve element movements that can be characterized as an insufficient opening stroke, or an insufficient sealing stroke. It is believed that this is because of the low thermal expansion characteristics of the length-changing actuator as compared to the thermal expansion characteristics of other fuel injector or engine components. For example, it is believed that a difference in thermal expansion of the housing and actuator stack can be more than the stroke of the actuator stack. Therefore, it is believed that any contractions or expansions of a valve element can have a significant effect on fuel injector operation
It is believed that there is a need to provide thermal compensation that overcomes the drawbacks of conventional methods.
The present invention provides a fuel injector that utilizes a length-changing actuator, such as, for example, an electrorestrictive, magnetorestrictive or a solid-state actuator with a compensator assembly that compensates for thermal distortions, brinelling, wear and mounting distortions. The compensator assembly utilizes a minimal number of elastomer seals so as to reduce a slip stick effect of such seals while achieving a more compact configuration for a compensator assembly. In one preferred embodiment of the invention, the fuel injector comprises a housing having a first housing end and a second housing end extending along a longitudinal axis, the housing having an end member disposed between the first and second housing ends; a length-changing solid state actuator disposed along the longitudinal axis. A closure member coupled to the length-changing actuator, the closure member being movable between a first configuration permitting fuel injection and a second configuration preventing fuel injection, and a compensator assembly that moves the length-changing actuator with respect to the housing in response to temperature changes. The compensator assembly includes a body. The body includes an interior surface defining a first fluid reservoir and a second fluid reservoir that are disposed between a first body end and a second body end, a valve spacer disposed between the first fluid reservoir and the second fluid reservoir. The valve spacer has a first spacer face and a second spacer face, and a plate contiguous to one of the first and second faces. The plate is responsive to one of a first fluid pressure in the first fluid reservoir and a second fluid pressure in the second reservoir so as to permit fluid flow from one of the first and second fluid reservoirs to the other of the first and second fluid reservoirs.
The present invention provides a compensator that can be used in a length-changing actuator, such as, for example, an electrorestrictive, magnetorestrictive or a solid-state actuator so as to compensate for thermal distortion, wear, brinelling and mounting distortion of an actuator that the compensator is coupled to. In a preferred embodiment, the length-changing actuator has first and second ends. The compensator assembly includes a body having a first body end and a second body end extending along a longitudinal axis. The body has a body inner surface facing the longitudinal axis, a first piston disposed in the body proximate one of the first body end and second body end, the first piston including a first face having a first surface area, a first sealing member coupled to the first piston and contiguous to the body inner surface, a second piston disposed in the body distal to the first piston, the second piston including a second face having a second surface area, a second sealing member coupled to the second piston and contiguous to the body inner surface, a spacer disposed between the first piston and the second piston in the body. The spacer has a first spacer end and a second spacer end in fluid communication with one another, the first spacer end being disposed in a confronting arrangement to one of the first face and second face so as to define a first fluid reservoir within the body, the second spacer end being disposed in a confronting arrangement to the other of the first face and the second face so as to define a second fluid reservoir within the body. A valve is disposed in one of the first and second reservoir, the valve being responsive to one of a first fluid pressure in the first fluid reservoir and a second fluid pressure in the second reservoir so as to permit fluid flow from one of the first and second fluid reservoirs to the other of the first and second fluid reservoirs.
The present invention further provides a method of compensating for distortion of a fuel injector due to thermal distortion, brinelling, wear and mounting distortion. The fuel injector includes a housing having a first housing end and a second housing end extending along a longitudinal axis, the housing having an end member disposed between the first and second housing ends, an length-changing actuator disposed along the longitudinal axis, a closure member coupled to the length-changing actuator, the closure member being movable between a first configuration permitting fuel injection and a second configuration preventing fuel injection, and a compensator assembly that moves the length-changing actuator with respect to the body in response to temperature changes. The compensator assembly includes a body having a first body end and a second body end extending along a longitudinal axis. The body has a body inner surface facing the longitudinal axis, a first piston disposed in the body proximate one of the first body end and second body end, the first piston including a first face having a first surface area, a first sealing member coupled to the first piston and contiguous to the body inner surface, a second piston disposed in the body distal to the first piston, the second piston including a second face having a second surface area, a second sealing member coupled to the second piston and contiguous to the body inner surface, a spacer disposed between the first piston and the second piston in the body. The spacer has a first spacer end and a second spacer end in fluid communication with one another, the first spacer end being disposed in a confronting arrangement to one of the first face and second face so as to define a first fluid reservoir within the body, the second spacer end being disposed in a confronting arrangement to the other of the first face and the second face so as to define a second fluid reservoir within the body. A valve is disposed in one of the first and second reservoir, the valve being responsive to one of a first fluid pressure in the first fluid reservoir and a second fluid pressure in the second reservoir so as to permit fluid flow from one of the first and second fluid reservoirs to the other of the first and second fluid reservoirs. In a preferred embodiment, the method is achieved by containing a predetermined amount of hydraulic fluid in the first and second fluid reservoirs; pressurizing the hydraulic fluid in at least one of the first and second fluid reservoirs so as to displace the first piston; and preventing communication of hydraulic fluid between the first and second fluid reservoirs during activation of the length changing actuator.